What makes a YouTube star?

A YouTube star is not a celebrity but “a friend” to the audience.

  

An “authentic” personality who speaks about ordinary human experience.

Uses low production values...
 
Is intensely focused on distribution... 

Has a subscriber base..

 

...and actively cross-promotes content on multiple social platforms.
 

For example...

Jenna Marbles is a self-described “blogger and entertainer” who has uploaded about 200 of her homemade videos since 2010. According to the New York Times she is one of the few content creators to reach more than one billion hits on YouTube and twelve million subscribers.

She is not a celebrity (well, she is now) and she writes and shoots most of her videos herself in her apartment using her laptop; very low production values. 

But: she is talented and funny (and uses a lot of profanity); she is “a friend” to the audience, an authentic personality who speaks about ordinary human experiences in a very amusing way; her weekly topics include: "Interrupting Adele" (10 million views); Drunk Makeup Tutorial" (17 million); "What Girls Do in the Bathroom in the Morning" (25 million); "What Girls Do in Cars" (32 million).

She actively cross-promotes her weekly content, promoting it on multiple social platforms including Facebook, Twitter and Instagram, and gets around 1 million views a day. 

As of 2013 (estimated by Comscore) YouTube has paid Jenna Marbles about $350,000 dollars for her videos.